(1) Field of the Invention
The present invention relates to the manufacture of semiconductor devices, and in particular, to a real-time monitoring of vaporization and liquid flow rate of precursor liquid components used in the formation of thin films on semiconductor substrates in an AMAT TEOS-based Dxz Chamber.
(2) Description of the Related Art
It is common practice to process thin films in chambers manufactured by Applied Materials, Inc., (AMAT). These chambers provide various controls in order to achieve stable operations such as having uniform thickness and topography of the resultant films. As is described more in detail below, factors contributing to the stability of the properties of the films include the flow rate of the precursor liquids that are vaporized to deposit the desired films on a substrate, as well as the continual vaporization process. It has been the experience in the present manufacturing line that it is difficult to detect a malfunction in the vaporization process with the AMAT TEOS-based Dxz Chamber, and, therefore, a real-time monitor mechanism has been developed which is disclosed later in the embodiments of the present invention.
In U.S. Pat. No. 5,531,183 by Sivaramakrishnam, et al., issued to Applied Materials, Inc., a vaporization sequence is disclosed for multiple liquid precursors used in semiconductor thin film applications. This sequence is formulated in order to reduce the temperature sensitivity of the respective liquid precursors in either the vapor or liquid state. The need for such a sequence is described because of the nature of processing thin films as follows:
Liquid source precursors or components are often used in processing thin films, such as, for example, silicon oxide films. These liquids are typically stored in source tanks and a re delivered as vapors to a deposition chamber using a delivery system wherein each liquid flows through a separate line and liquid flow meter (to provide individual control of the flow rate of each reactant) and then is injected as a vapor into a common manifold. The vapors flowing in the manifold are then introduced into processing chamber connected to the manifold downstream of the points of entry of the gases and vaporized liquid source precursors into the manifold.
While the vaporous components, upon entering the processing chamber, perform satisfactorily, for example to form a thin film on a semiconductor substrate, it has been found that problems of either condensation of the previously vaporized liquid source component(s) or boiling of the still liquid component(s) in the delivery system can occur, depending upon the temperatures maintained at various points in the delivery system, including along the manifold. For example, if the temperature at a particular point along the manifold is too low (a cold spot), condensation of a previously vaporized liquid precursor source or component may occur at that point in the manifold. On the other hand, maintenance of too high a temperature in the manifold (to prevent such undesirable condensation) can result in boiling/decomposition of a liquid component in the liquid supply line of the particular liquid component upstream of its vaporization and injection into the manifold. This, in turn, can lead to instabilities in the flow rate control of that particular component due to fluctuations of the liquid flow meter as the boiling or near boiling component flows through it.
For example, Sivaramakrishnam, et al., describe that in the formation of a thin film of silicon oxide on a semiconductor substrate for use as a planarization layer, the silicon oxide is usually doped with phosphorus and/or boron to enhance the flow characteristics of the silicon oxide during a subsequent planarization step. This results in the use of a liquid silicon source precursor, such as an alkoxysilane, e.g., tetraethylorthosilicate (TEOS), a liquid phosphorus source precursor such as, for example, trimethylphosphite (TMP), triethylphosphite (TEP), or triethylphosphate (TEPO); and/or a liquid boron source precursor such as, for example, trimethylborate (TMB) or triethylborate (TEB).
Following Sivaramakrishnam, in a vaporization system such as shown in FIG. 1, these liquids are stored in separate source tanks ((10a), (10b), (10c)) and are delivered as vapors to a deposition chamber using a delivery system wherein the liquid sources of silicon, phosphorus, and boron flow through separate lines ((20a), (20b), (20c)), liquid flow meters ((30a), (30b), (30c)) into valves ((40a), (40b), (40c)) and then are respectively injected as vapors into a common manifold (50) where they are usually mixed with a carrier gas from its own tank (60) flowing through its own flow meter (63) and valve (65) into the common manifold, which in turn leads the mixture to distribution nozzle (55) in the chamber. The vapors flowing in the manifold are then further mixed with a vapor source of oxygen in tank (70), usually just prior to entry into deposition chamber (80) to avoid premature reaction, to form the doped silicon oxide film on the semiconductor substrate (90) held on a heated holding fixture (85) in the deposition chamber. Typically the reaction may be either a thermal CVD reaction or a plasma-enhanced CVD reaction. The presence of the dopants in the resulting silicon oxide film lowers the temperature at which the silicon oxide film may be subsequently reflowed to produce a planarized film.
While the vaporous components, such as the reactants described above, react in a deposition chamber to form a satisfactory doped silicon oxide film useful for planarization of a structure formed on a semiconductor substrate, Sivaramakrishnam, et al., report that problems of either condensation or boiling in the delivery system can occur. As described above, if the temperature at a particular point along the manifold is too low, condensation of a previously vaporized reactant may occur at that point in the manifold, while maintenance of too high a temperature in the manifold can result in boiling/decomposition of a liquid precursor in the liquid supply line of that reactant upstream of its vaporization and injection into the manifold, resulting in erratic flow of the liquid precursor through the liquid flow meter.
The resultant instabilities in the flow rate of the reactants, due to either problem, can interfere with the satisfactory formation of a homogeneous product such as a properly doped silicon oxide film. For example, in the above described formation of a phosphorus and/or boron-doped silicon oxide film, premature condensation can effect incorporation of one or more of the dopants into the film, as well as effecting the uniform distribution of the dopant(s) in the silicon oxide film. Additionally, each microlayer of the thin film of silicon oxide could incorporate different concentrations of the respective dopants if the vaporization rates and flow into the processing chamber are not uniform.
It is, therefore, suggested by Sivaramakrishnam, that it would be advantageous to design a component delivery system used in the processing of thin films on semiconductor substrates, and in particular a component delivery system which utilizes liquid precursors, which would reduce the temperature sensitivity of the respective components in either the vapor or liquid state.
Another U.S. Pat. No. 6,179,277 by Huston of AMAT provides for improved liquid vaporizer systems and methods for their use. Vaporizer systems of the invention are particularly useful for the vaporization of liquids having a relatively low vapor pressure, such as tetrakisdiemthyl-amidotitanium (TDMAT). In one embodiment, a liquid vaporizer system includes a vaporizer unit having first and second inlets and an outlet. The vaporizer system further includes a vessel having an inlet and an outlet, whereby the vessel inlet is operably connected to the vaporizer outlet. The vessel contains a plurality of passages which operably connect the vessel inlet and the vessel outlet. In this manner, liquids and/or gases flowing into the vaporizer unit through either or both of its two inlets, exit the vaporizer unit outlet and enter
the vessel inlet. Liquids and/or gases pass through the plurality of passages and exit the vessel outlet. In this manner, heating vaporizer unit and vessel to desired temperatures results in the vaporization of the liquid, such as liquid TDMAT.
Another apparatus by AMAT, namely, a liquid phosphorous precursor delivery apparatus is described in U.S. Pat. No. 5,925,189 by Nguyen et al., where the invention recognizes that the build-up of residue in a metal alloy injection valve used to inject a liquid phosphorous precursor compound is due to the nickel in the alloy affecting the liquid phosphorous precursor compound. The invention thus provides components manufactured of an alloy having a low nickel content, preferably less than 5% nickel, and more preferably less than 1%. In an additional aspect of the invention, the alloy is provided with a higher chromium content, preferably at least 15% chromium, more preferably 16-27%.
As these vaporizer, or, vaporization, systems are used for the important function of depositing thin films on wafers, what is needed is a method for quickly assessing the quality of the vaporization process and assuring that full vaporization takes place in the system so that thin films of required properties are obtained, and scrapped wafers are avoided as a result.